The transcription factor NF-E2 and the gene encoding PRV-1 are overexpressed in patients with polycythemia vera (PV). The recent description of a Jak2V617F mutation in PV patients raises the question whether this allele exerts its effect on the malignant clone in part through inducing NF-E2 expression. NF-E2 is a promising candidate in the pathophysiology of PV for several reasons: NF-E2 is overexpressed in stem cells as well as in all three cell lineages affected in PV. In murine cells NFE2 overexpression leads to Epo-independent growth and differentiation. NF-E2 may thus play a pivotal role in causing the erythrocytosis of PV. However, both the molecular mechanism leading to NF-E2 overexpression and its effect on human hematopoiesis are not known. In addition, the cause of PRV-1 overexpression remains unclear. Therefore, it is the aim of this project to investigate the cause of NF-E2 and PRV-1 overexpression in PV and the effect of NF-E2 overexpression in hematopoietic cells. Based on the following hypotheses, the specific aims of this project are therefore: 1. Hypothesis: NF-E2 is required for the Epo-independent growth of PV cells or its overexpression modulates hematopoietic differentiation. Specific Aim: To modulate NF-E2 expression via siRNA knock down and retroviral or lentiviral transduction and examine the consequences on Epo-dependent and -independent growth in vitro. 2. Hypothesis: NF-E2 and PRV-1 overexpression in PV are mediated by the Jak2V617F allele Specific Aim: To introduce Jak2 wt and V617F alleles in vivo and in vitro and examine the effects on NF-E2 and PRV-1 expression in various models. 3. Hypothesis: NF-E2 and PRV-1 overexpression result from aberrant transcriptional activation Specific Aim: To characterize protein/DNA interaction on the NF-E2 and PRV-1 promoters in PV and healthy control cells to determine aberrantly activated transcription factors. Public Health Implications: By leading to a better understanding of the molecular changes that lead to the development of PV, this project will point out molecules against which new drugs for treatment can be developed.